1. Field of the Invention
The invention relates to gyrasphere crushers and, more particularly, relates to gyrasphere crushers having a crushing head, a crusher bowl which is vertically adjustable relative to the head, and a bowl lock assembly which normally prevents vertical adjustment of the bowl relative to the head but which selectively permits such adjustment.
2. Discussion of the Related Art
Gyrasphere crushers typically include a stationary frame, a generally conical crushing head mounted in the frame for rotation about an eccentric shaft and including an upwardly facing convex crushing surface, and an annular crusher bowl that is mounted on the frame above the head so as to define a crushing gap therebetween forming an annular crushing chamber. Material to be crushed is fed downwardly into the crushing chamber and is crushed by gyration of the head about the eccentric.
The particle size of the output from the crusher is dependent upon the thickness of the crushing gap. Particle size adjustment and/or compensation for wear on the opposed surfaces of the head and the bowl is thus possible by mounting the bowl on the crusher frame for vertical movement with respect thereto whereby the crushing gap is widened by raising the bowl or narrowed by lowering it. To permit such adjustment, the frame of the bowl is threadedly connected to an upper portion of the crusher frame, and the bowl is vertically adjusted by rotating it in the appropriate direction relative to the crusher frame.
When satisfactorily adjusted, the bowl must be locked or prevented from rotating relative to the crusher frame in response to the tangential forces imposed upon it by the gyrating head. This locking is typically performed via a threaded locknut or clamping ring which is located just above the threaded portion of the bowl frame and which is threadedly connected to the crusher frame so as to be selectively operable as a conventional locknut or jam nut. A substantial clamping force is normally exerted between the bowl and the locknut to urge them axially towards one another. For adjusting rotation of the bowl, this clamping force must of course be released.
Various arrangements or lock assemblies have been proposed for providing the necessary clamping force between the bowl and the locknut and for selectively releasing this clamping force. Early crushers employed a complex system of wedges for applying the clamping force, and these wedges had to be removed to permit adjustment. Such lock assemblies, an example of which is disclosed in U.S. Pat. No. 2,881,981 to Rumpel, proved complex and difficult to operate and soon were replaced with mechanically applied/fluid-pressure released lock assemblies which remain in wide use today.
Mechanically applied/fluid-pressure released lock assemblies typically employ a system of Belleville washers or other mechanical springs to apply clamping forces to the locknut. These forces are released by action of a plurality of single or double-acting hydraulic cylinders spaced around the locknut. Examples of mechanically applied/fluid-pressure released lock assemblies and their variants are disclosed, e.g., in U.S. Pat. Nos. 3,341,138 to Allen, 3,797,760 to Davis et al., 3,951,348 to Davis et al., 4,198,003 to Polzin et al., and 4,478,373 to Gieschen.
Mechanically applied/fluid-pressure released lock assemblies for gyrasphere crushers exhibit several drawbacks and disadvantages. Most notably, adjusting "on the fly," i.e., when the crusher is crushing rock (typically referred to as operating "under load") is difficult or impossible. Adjusting under load is desirable because crushers typically form but one component of a relatively large quarrying system with the crusher continuously receiving stone from upstream devices such as screens and supplying the crushed stone to downstream devices. Shutting down the crusher for adjustment therefore requires that the feed be shut down, thereby significantly increasing down time and operating costs. Adjusting under load is as a practical matter made difficult with crushers employing mechanically applied/fluid pressure released lock assemblies because there is a high amount of uncertainty as to the release point of such systems, (The release point is defined as that point at which the net clamping force applied by the mechanical springs as offset by the release forces supplied by the fluid actuated cylinders produces a rotational locking force which is just below the rotational forces supplied by bowl adjuster mechanisms). Uncertainty exists because spring forces vary from system to system and actually vary in a given crusher over the life of the springs because the spring rate decreases as the springs age. Given this uncertainty, it is typically necessary to fully or nearly fully release the clamping forces each time adjustment is required thereby preventing "feathering," i.e., relatively minute adjustments which do not significantly affect the current operation of the crusher. The need has therefore arisen to provide a lock assembly the net clamping forces imposed by which can be precisely controlled to permit adjustment of the bowl under load.
Another disadvantage associated with conventional mechanically applied/fluid-pressure released lock assemblies is that the cylinders apply the release forces over a very small area and thus must operate under extremely high pressures, typically on the order of 7000 psi or more. Operating under such high pressures requires the use of relatively expensive high pressure fittings and hoses and renders the system more prone to leaks. The need has therefore arisen to permit the release of lock assemblies for crushers using relatively low fluid pressures.